Fertilizers are materials added to soils to supply elements required for plant nutrition. They may be products manufactured for the purpose, by-products of the manufacture of other chemicals, or natural materials. Fertilizer consumption has increased rapidly in the last quarter century and fertilizers manufactured for agricultural purposes have become a major product of the chemical industry world-wide.
Plants require several materials for adequate nutrition. The principal ones, carbon dioxide and water, are usually available in adequate amounts from the atmosphere and soil, and are continually replenished by natural means. Other essential nutrients are normally available in the soil but are not replenished by nature after plant utilization. Agricultural areas can as a result of intensive cultivation be substantially depleted of important nutrients. In addition to carbon, hydrogen and oxygen, 13 nutrients have been identified as essential to plant nutrition, including nitrogen, phosphorous, potassium, calcium, magnesium, sulphur, iron, manganese, copper, zinc, boron, molybdenum and chlorine. Of these elements, nitrogen, phosphorous and potassium are needed by plants in relatively large quantities and are called major elements or macronutrients. Calcium, magmesium and sulphur are normally required in lesser amounts and are considered secondary nutrients, while the remaining elements are known as micronutrients or trace elements because their requirements are very small.
The fertilizer elements discussed above are most commonly applied to the soil in the form of ammonia (NH.sub.3), ammonium nitrate (NH.sub.4 NO.sub.3), ammonium sulfate ([NH.sub.4 ].sub.2 SO.sub.4), urea ([NH.sub.2 ].sub.2 CO), sodium nitrate (NaNO.sub.3), calcium nitrate (Ca(NO.sub.3).sub.2), ammonium chloride (NH.sub.4 Cl), monocalcium phosphate (CaH.sub.2 [PO.sub.4 ].H.sub.2 O), dicalcium phosphate (Ca.sub.2 HPO.sub.4), potassium chloride (KCl), potassium sulfate (K.sub.2 SO.sub.4), monoammonium phosphate (NH.sub.4)H.sub.2 PO.sub.4, diammonium phosphate (NH.sub.4).sub.2 HPO.sub.4, and others.
Fertilizers have been encapsulated using resinous encapsulating agents in order to provide slow release of the fertilizer compositions into the environment. However, many of the encapsulation processes produce a product which is prohibitively expensive for agricultural purposes. Most agricultural fertilizers are commodity chemicals which are very low in cost.
One problem that exists with most common fertilizers is that they tend to release nitrogen and other fertilizing components rapidly into the soil. The rapid release of the fertilizing components can tend to harm plant roots and stems and can often result in growth of plant parts which are not desirable, such as stems and leaves, at the expense of reduced yield.
Further, many fertilizer compositions such as ammonium nitrate can be explosive in concentrated form. Accordingly, a substantial need exists to provide an encapsulated slow release fertilizer composition means which can release fertilizer elements at a rate such that the plant is not harmed and the fertilizer is utilized by the plant for improving crop yield.